Cables, such as telephone lines, that are placed below the ground are usually enclosed in a sheath and internally pressurized with dry air. Dry Air is feed into air pipe and is then feed at predetermined locations along the cable into the sheath. By pressurizing the sheath in which the cables lie, it aids in preventing water from shorting pairs of the wires that make up the cables. Unfortunately, there are times when the sheath or air pipe are penetrated, either by chemical degradation (electrolysis), mechanical stresses, or similar phenomena. Penetrations in the sheath could permit water to seep inside should the internal pressure fall below the head pressure of the water above the cable sheath. Water, then causes a degradation of any internal insulation. After the insulation is exposed, water then makes it way into the bare cable. This, in turn, causes the wire to short as well as degradation of the signals carried by the cable. Leaks in the Air Pipe also effect the air pressure level within the cable sheath also. If the pressure drops low enough within the air pipe, water can seep inside the cable sheath.
Discovering and repairing this damage can cost the provider substantial sums of money. One of the reasons is that it is sometimes necessary to excavate in several points. Another reason is that the it might be necessary to unearth hundreds of cubic yards of earth due to the impossibility of identifying the exact location of the leak.
Another technique is to introduce a detectable tracer gas into the cable and let it permeate to the surface. A mass spectrometer is then used to detect the tracer gas. The problem with the spectrometers is that their operation depends upon separation of the tracer gas in a vacuum by imparting an electrical charge to the gas sample containing the tracer helium. The sample is pushed through a magnetic field, and the hydrogen ions collected from the results. The electronics, in such a device, include a supply of high voltage and the vacuum system. All of these components tend to make the helium detector bulky, complicated and expensive. With this type of equipment, it is difficult to operate the detector in areas where access to such heavy equipment can be difficult.
An additional problem with the prior art was the ability to accurately detect the tracer gas. In many of the prior art devices, other non-tracer gases had the ability to set-off the detector.
Accordingly, it is desirable to provide an efficient method and apparatus to be able to determine air flow within an air pipe. It is also desirable to provide a method apparatus that can leave a valve in an air pipe and take advantage of the pressurized line and accurately determine the location of the break in the air pipe or cable by using flow analyses techniques. Additionally, it is desirable to provide an open flow and restricted flow path in one apparatus.